WithOsEnv assumes wrongly that os.Environ() returns only strings containing an equal sign

[apostasie]

https://github.com/compose-spec/compose-go/blob/main/cli/options.go#L240

This will call GetAsEqualsMap which will throw with an index out of bound in case a string does not contain an equal sign.

(we did hit that with a broken test in nerdctl - https://github.com/containerd/nerdctl/pull/3111)